Recently, along with a recent tendency of reducing business trip costs and business trip man hours, transmission systems for carrying out a TV conference using a communication network such as the Internet have become spread. In such a transmission system, when a telephone call is carried out between plural transmission terminals, image data and voice data are transmitted therebetween, and thus, a TV conference can be carried out.
Further, by displaying a destination list on the side of a request source terminal which is a request source of a telephone call for the purpose that the user of the request source terminal can easily select a desired destination terminal from among plural candidates for the telephone call, the user of the request source terminal can select the desired destination terminal (see Japanese Laid-Open Patent Application No. 2006-074453).
However, a first user may be troubled when a second user registers the transmission terminal of the first user in the second user's destination list without approval from the first user, and the first user receives a start request for a telephone call from the second user.